1. Field of the Invention
The invention relates to safety apparatus for preventing buckling of pinning rods used with underground mine-shaft roof-bolting machines.
2. The Prior Art
Hydraulically-operated roof-bolting machines for underground mine shafts have been known for some time. Such machines typically have a torque motor, a pinning rod held for rotation by the torque motor, a hydraulic device for exerting upward thrust on the torque motor to force the pinning rod upwardly into the roof of a mine shaft, and a device for manually controlling the upward thrust device. Many of the roof bolters which are now commercially available have a hydraulically operated boom for raising the torque motor, the boom including a linkage arrangement for maintaining the pinning rod in a vertical position. One commercially-available roof bolter has a hydraulic cylinder for raising the torque motor, the hydraulic cylinder being here directly mounted on the roof bolter frame or, in some cases, mounted on the end of a hydraulic boom.
In addition, devices are known for hydraulically controlling the rate of pinning-rod infeed so as to increase the drilling rate for softer rock and decrease the drilling rate for hard spots. For example, U.S. Pat. No. 2,320,874 to Lehmann controls the infeed rate and includes a threshold level pressure cutoff which stops the infeed when the pressure in the feed cylinders builds up beyond a predetermined level.
Another type of automatic feed-pressure regulator is shown in U.S. Pat. No. 2,322,741 to Osgood. In this device, the feed control means is automatically responsive to variations in the resistance to drill bit penetration. An arrangement for providing optimum feed force to the mining drill in a pneumatic system is shown in U.S. Pat. No. 2,754,804 to Miller.